[petsc-users] A question on Schur complement

Jed Brown jed at jedbrown.org
Fri Jan 26 14:09:14 CST 2018

saturday luis <luis.saturday at gmail.com> writes:

> Hi PETSc team:
> I want to consult for a good way of doing an approximated Schur complement
> matrix. So I just want to handle a matrix in the format C + B^t B, or
> sometimes B^t B.
> An easy way is to run with the MatCreateSchurComplement to create C + B^t
> inv A B, wherein A is an identity matrix. The downside is that the matrix
> free style does not allow for algebraic preconditioners.

MatCreateLRC is more natural in this context.

Even if you solve with LSQR, you'll likely need some explicit
representation for preconditioning.

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